It is known in the art, such as in U.S. Pat. No. 5,806,794 and US 2016/0107747 A1 for aircraft landing gear to comprise a number of bogies, each connected to an attachment portion of a shock strut's piston (often referred to as the piston fork), that retract during flight. The aircraft bogies comprise at least two wheels connected to one another by a bogie beam, in a balanced fashion whereby the shock strut is arranged in a central position with at least one wheel behind and at least one wheel in front of the shock strut when viewed in the direction of travel.
As illustrated in U.S. Pat. No. 5,806,794 and US 2012/0256050, a horizontal brake rod or pair of brake rods may connect at a central point along the bogie to a base of the attachment portion or piston fork which protrudes below the bogie beam. The brake assemblies are usually arranged to “float” around the wheel axles and the brake rod (or rods) reacts torque on the brake assemblies under braking conditions of the aircraft.
In these known arrangements, the brake rod, at least when the landing gear is deployed, is offset vertically below the axes of rotation of the aircraft wheels. When the brakes of the aircraft are applied, the brake rod experiences a tensile force from the rear wheel since the torque on the rear brake assembly is pulling away from the brake rod at the point of contact, and a compressive force from the forward wheel, as the torque on the forward brake assembly at that point is pushing towards the brake rod.
As the brake rod will have portions acting in tension and compression, the portion of the brake rod in compression must be made strong enough to resist buckling. This may mean the brake rod is sized to meet the expected loads of the forward portion of the brake rod which is subjected to compressive forces, leading to overcompensation in terms of size and weight for the rear portion of the brake rod which is subjected to tensile forces.
US 2014/0084108 A1 discloses a possible means for overcoming this problem. The forward end of the brake rod is attached to the top of the forward brake assembly and a rear end is connected to the bottom of a rear or following brake assembly. As a result, the brake rod extends at an angle, sloping downwards from the front to the rear, such that both the forward and rear portions of the brake rod experience a tensile force during braking.
The brake rod may be a single rod with forward and rear brake portions, or may comprises separate forward and rear rods. In all cases, the brake rod which is attached to the top of the forward brake assembly has a central connection point (where central is with reference to a central portion along the bogie beam) to react the opposing tensile forces into the bogie beam or an axle thereof and to stabilise the position of the brake assemblies.
Since both portions of the brake rod will experience a tensile force during braking, the brake rod can be made more slender, reducing weight in the landing gear despite the additional length of the forward brake rod.
Although the above provides a means for reducing the size of the brake rod, the attachment positions on the bogie beam or axle can experience high levels of shear, if for any reason the tensile forces are not balanced (e.g. in the event of a brake failure). Accordingly, to accommodate the potential shear loads, the bogie beam may need to be made bigger and stronger and so some of the weight savings may be diminished.
It is desirable to reduce landing gear weight further, for example, where possible by improving aircraft design so that composite parts can replace the current metal sections. The present disclosure addresses at least some of the above problems.